EICIC Configuration Algorithm with Service Scalability in Heterogeneous Cellular Networks

In this paper, a joint control method for the user association and almost blank sub-frame (ABSF) based interference coordination (IC) technique in heterogeneous cellular networks is proposed. The optimization objective is simultaneously improving system throughput and guaranteeing proportionally fairness. Usually, user and base station (UE-BS) association is performed before ABSF rate determination, which is suboptimal with respect to UE- BS association. We formulate the joint optimization of UE-BS association and ABSF rate as a combinatorial optimization problem. To deal with it, we proposed an iterative method to discover the ABSF rate, the optimal association and the optimal resource blocks(RBs) allocation that can maximum long-term average throughput. Besides, as we cannot know the interference before user-association and resource allocation, we proposed a graph-based BS clustering method to estimate the interference before user-association and resource allocation. Simulation results show the efficiency of our proposed scheme.

An LTE-Advanced (LTE-A) Heterogeneous Network (HetNet) constitutes of a macro cell and small cells, where, the former acts as an overlay network and the latter as an underlay network. In HetNet, enabling Carrier Aggregation (CA) usually results in severe downlink interference at small cells from macro cell because of high powered transmissions from macro cell on over-lapping component carriers (co-channels). The intensity of downlink interference is much more profound in HetNet enabled with CA than compared with a single carrier HetNet and ultimately affects the Quality of Service (QoS) of users connected to small cells. Some frequency domain solutions like cross carrier scheduling, soft frequency reuse, and downlink power control have been proposed so far, but they do not provide complete orthogonal transmissions among macro and small cells, leading to adjacent channel interference. Also, a few time domain approaches like Almost Blank Subframe (ABS), dynamic ABS have been proposed in the literature. However, the resource utilization of cells decreases due to high number of ABS assignments in the dense deployment, which also results in low user throughput. In this paper, we propose a combined time domain and frequency domain novel idea for downlink interference control, which is via adaptive Discontinuous Reception (DRX) settings through Multi-Objective optimizations and an optimal carrier allocation scheme, respectively. The proposed idea mitigates the downlink co-channel interference by enabling intermittent data reception at the User Equipment (UE) through adaptive DRX settings, also it utilizes an effective carrier allocation scheme such that users are always allocated to carriers with least interference. The analytical model and simulation results reveal that the proposed idea achieves average gain of 3.5 times w.r.t cell throughput when compared with well-known downlink interference mitigation schemes.

The rate distribution in heterogeneous networks (HetNets) greatly benefits from load balancing, by which mobile users are pushed onto lightly-loaded small cells despite the resulting loss in SINR. This offloading can be made more aggressive and robust if the macrocells leave a fraction of time/frequency resource blank, which reduces the interference to the offloaded users. We investigate the joint optimization of this technique - referred to in 3GPP as enhanced intercell interference coordination (eICIC) via almost blank subframes (ABSs) - with offloading in this paper. Although the joint cell association and blank resource (BR) problem is nominally combinatorial, by allowing users to associate with multiple base stations (BSs), the problem becomes convex, and upper bounds the performance versus a binary association. We show both theoretically and through simulation that the optimal solution of the relaxed problem still results in an association that is mostly binary. The optimal association differs significantly when the macrocell is on or off; in particular the offloading can be much more aggressive when the resource is left blank by macro BSs. Further, we observe that jointly optimizing the offloading with BR is important. The rate gain for cell edge users (the worst 3-10%) is very large - on the order of 5-10x - versus a naive association strategy without macrocell blanking.

Range expansion and inter-cell interference coordination can improve the capacity and fairness of heterogeneous networks by off-loading macrocell users to low-power nodes like picocells. In contrast to previous studies, which rely mostly on simulations, we here consider analytical models for base station and user (UE) locations in a macro network with pico-cell overlay and derive closed-form expressions for the distribution of the signal to interference plus noise ratio (SINR) and spectral efficiencies (SEs) of UEs associated with macro- and pico-cells. These results illuminate the effects on SE of (i) duration of the macro almost blank subframes (ABSs), (ii) the SINR threshold for a UE to be served by a picocell during ABSs, and (iii) the range expansion bias. They also help determine the optimum settings of these parameters.

How many small cell (SC) access points (APs) are required to guarantee a chosen quality of service in a heterogeneous network? In this chapter, we answer this question considering two different network models. The first is the downlink of a finite-area SC network where the locations of APs within the chosen area are uniformly distributed. A key step in obtaining the closed-form expressions is to generalize the well-accepted moment matching approximation for the linear combination of lognormal random variables. For the second model, we focus on a two-layer downlink heterogeneous network with frequency reuse-1 hexagonal macro cells (MCs), and SC APs that are placed at locations that do not meet a chosen quality of service from macro base stations (BSs). An important property of this model is that the SC AP locations are coupled with the MC coverage. Here, simple bounds for the average total interference within an MC makes the formulation possible for the percentage of MC area in outage, as well as the required average number of SCs (per MC) to overcome outage, assuming isolated SCs. Introduction Heterogeneous cellular networks (HCNs) are being considered as an efficient way to improve system capacity as well as effectively enhance network coverage [1, 2]. Comprising multiple layers of access points (APs), HCNs encompass a conventional macro cellular network (first layer) overlaid with a diverse set of small cells (SCs) (higher layers). Cell deployment is an important problem in heterogeneous networks, both in terms of the number and positioning of the SCs. Traditional network models are either impractically simple (such as the Wyner model [3]) or excessively complex (e.g., the general case of random user locations in a hexagonal lattice network [4]) to accurately model SC networks. A useful mathematical model that accounts for the randomness in SC locations and irregularity in the cells uses spatial point processes, such as Poisson point process (PPP), to model the location of SCs in the network [5–10]. The independent placement of SCs from the MC layer, has the advantage of analytical tractability and leads to many useful SINR and/or rate expressions. However, even assuming that wireless providers would deploy SCs to support mobile broadband services, the dominant assumption remains that SCs are deployed randomly and independent of the MC layer [11].

The enhanced Inter-Cell Interference Coordination (eICIC) techniques introduced for LTE-Advanced HetNets yield significant gains by offloading macro cell users to small cells. Interference management is enabled via Almost Blank Subframes (ABS) on which the high power macro cells mute. This creates two different interference patterns corresponding to non-ABS and ABS subframes, which makes analyzing resource allocation and throughput performance non-trivial. We introduce a utility model for the eICIC framework that enables us to study resource allocation with different interference patterns. We use a semi-analytical method using this model to study resource allocation of pico cell-center users on both non-ABS and ABS subframes. We show for proportional fairness, the pico cell-center users may need to be scheduled on ABS subframes. We also demonstrate that this model can be used to determine the optimal ABS configuration for a given deployment.

이종 네트워크 환경에서 이종셀 간 간섭 제어를 위해 Almost Blank Subframes (ABS)이 제안 되었다. ABS에서는 서브프레임에 대한 자원 할당을 하지 않음으로써 동일 채널 간섭을 줄일 수 있다. 기존 연구에서는 ABS 기술의 성능 평가를 위한 수학적 모델링이 제안되지 않았다. 본 논문에서는 ABS 기술에 대한 수학적 모델을 제시하였다. 분석을 위한 가정에서 OFDMA 기반의 다중 반송파 (multi carrier) 시스템을 가정하였고, large-scale 페이딩을 가정하였다. 성능 평가로써 effective SINR에 대한 누적분포함수를 나타낸다. 시뮬레이션과 분석에 대한 결과 비교를 통해 수학적 모델에 대한 정확도를 보인다. In heterogeneous networks, the almost blank subframes (ABS) for inter-cell interference coordination (ICIC), which can be protected from the CCI due to unutilized subframes (i.e., ABS) is proposed. However, the analytical model for ABS-based systems has not been fully studied yet. In this paper, we derive a new analytical model to evaluate the performance of ABS-based systems. In an analytic model, we assume that each carrier in multicarrier systems, such as in OFDMA, is subject to large-scale fading, which is independent of other carriers. As a performance measure, we present the cumulative distribution function (CDF) for the effective SINR. We show the accuracy of the analytical model via simulation results.

Responding to the unprecedented challenges imposed by the 5G technologies, mobile operators have given significant attention to Heterogeneous Cloud Radio Access Networks (H‐CRAN) due to their beneficial features of performing optimization, cost effectiveness, and improving spectral and energy efficiency performance. H‐CRAN inherits the attractive benefits of Heterogeneous Networks (HetNet) and the cloud computing by facilitating interference mitigation, scalability, and radio resource control. Consequently, H‐CRAN is proposed in this article as a cost‐effective potential solution to alleviate intertier interference and improve cooperative processing gains in HetNets by employing cloud computing. H‐CRAN can provide efficient resource sharing at the spectrum, network, and infrastructure levels. Therefore, this article proposes H‐CRAN cooperative interference mitigation method that enhances the time sharing among Radio Remote Heads (RRH) users. The study proposes an enhanced Almost Blank Subframe (ABSF) technique to increase the SINR and throughput of the small‐cell (low power base station) and macrocell users. Simulation results show that the proposed Dynamic Programming‐Diverse Almost Blank Subframe (ABSF) Pattern (DP-DAP) scheme improved the macro‐ and small‐cell users up to 56% and 35%, respectively, as compared to other state‐of‐the‐art ABSF schemes.

Enhanced Inter-Cell Interference Coordination (eICIC) is used in LTE heterogeneous networks to reduce interference in the small cell expansion region. Service areas of small cells are often expanded by a Cell Selection Offset (CSO) to increase their traffic uptake and offload macro cell traffic. eICIC relies on Almost Blank Subframes (ABS) or Reduced Power Almost Blank Subframes (RP-ABS) to manage interference between macro and small cellular layers. Gains achieved from deploying intra-carrier small cells are highly dependent on the optimization of eICIC parameters. This paper provides a novel optimization formulation to achieve optimal small cell CSOs and macro cell ABS or RP-ABS patterns. The performance of the outlined optimization framework is evaluated by state-of-the-art LTE system level simulations. Simulation results indicate an average network capacity gain of 19.4% from optimizing ABS-eICIC parameters, and a 22.8% gain from optimizing RP-ABS-eICIC parameters. Similarly, a 42.2% average gain in user data rates is achieved from optimizing ABS-eICIC parameters, and a 45.9% gain from optimizing RP-ABS-eICIC parameters.

Traditional macro-cell networks are experienced an increase of data traffic and small-cells are deployed help to offload the traffic from macro-cells. The Energy Aware Traffic Offloading for Green Heterogeneous Networks (EATOG) approach is analyzed on grid power saving by offloading traffic for green heterogeneous networks to increase the efficient utilization of harvested energy for on-grid power saving while satisfying the Quality of Service (QoS) requirement. The EATOG is mainly intends to of energy-aware traffic offloading for HCN with multiple Small cell Base Station (SBS) powered by diverse energy sources which reduces the on-grid network power consumption while satisfying the QoS requirement in terms of rate outage probability. The performance of energy consumption is degraded due to the Overlapped Small Cell Based Stations. An optimal deploying low power node within macrocell coverage area is proposed in this paper to improve the system utility while minimizing the installation cost. The proposed Optimized Energy Aware Traffic Offloading for Green Heterogeneous Networks (OEATOG) approach is considers the inter-cell interference and the configuration of Almost Blank Sub-frames (ABS) when maximizing the system utility. The proposed paper deals with the placement of Pico Base Station within the macro cell in LTE (Long Term Evolution) heterogeneous networks. A Pico Cell is a small cellular Base Station (BS) which supports low power nodes and offers greater capacity and coverage areas. Furthermore the heuristic algorithm is introduced too efficiently solve the formulated problem and obtain the optimal picocell placement. The simulation results indicate that the proposed algorithm is to improve the utility of the network, especially in regions with high traffic density, while maintaining the installation cost at a reasonable level.

Heterogeneous network has recently been proposed as a promising approach for improving capacity and coverage. A large number of low power nodes will consume a lot of energy, which is not conductive to improve the network Energy Efficiency (EE). In this paper, in order to improve network EE, an energy-efficient time-frequency domain interference coordination algorithm is proposed. Firstly, a novel dynamic point blanking (DPB) scheme is proposed and introduced into almost blank subframe (ABS) scheme, which can dynamically mute the strongest interference of coordinated points in frequency domain. Secondly, an adaptive ABS configuration scheme configures proper ABS ratio and optimal transmission power according to the practical load. To efficiently implement the proposed scheme, a concept of cloud cooperated cellular network (C-HetNet) is introduced where low power pico base stations (BSs) overlaid on a macrocell are connected to cloud radio access network (C-RAN) to operate with the macro BS. The simulation results demonstrate that the proposed scheme can increase the total network EE excellently while ensuring fairness between macrocells and picocells.

Radio resource allocation (RA) in heterogeneous networks (HetNets) is an important problem. In this paper, we focus on two RA schemes proposed in the literature for future HetNets: almost blank subframes (ABS) and partially shared deployment (PSD). Through extensive analysis and simulations, we show that PSD outperforms ABS on many fronts across different α-fairness criteria and traffic scenarios.

Time-domain inter-cell interference coordination, so called eICIC, has been introduced in Long Term Evolution-Advanced (LTE-Advanced) system as a throughput improvement method for heterogeneous network, where a lot of low power nodes (LPNs) are located in the coverage area of high power base station (Marco-BS). eICIC enables Macro-BSs to configure almost blank subframe (ABS), in which Marco-BSs reduce their transmit power or mute data transmission so as to reduce interference to the users served by LPNs. However, the improvement of the overall throughput is affected by the ABS setting. This paper proposes a novel user throughput estimation method for LTE-Advanced system where ABS and proportional fairness scheduler are applied. Numerical results show that the proposed method accurately estimates the user throughput for arbitrary ABS ratio with the estimation error of 1-7% for cell edge user throughput and around 1% for average user throughput, respectively. As a result, using the proposed method, Macro-BSs can decide proper ABS ratio to maximize cell edge or average user throughput.

The 3GPP has proposed enhanced intercell interference coordination (eICIC) by making the macrocell silent in the almost blank subframes (ABSs) to mitigate interference for low-power base stations (BSs) in the downlink direction. However, two important challenges are introduced: 1) the underutilization for macrocell in ABS and 2) the optimal downlink association may not be optimal for uplink transmission, i.e., downlink/uplink decoupling (DUDe). In this paper, we first propose a novel method based on configuring uplink transmission in the macrocell in ABSs (UM-ABS) for eICIC to improve the efficiency of the ABS. Then, the UM-ABS and DUDe are formulated as an optimization problem of investigating the joint load balancing of downlink and uplink for eICIC in heterogeneous networks (HetNets) while considering different service classes. The problem is actually a mixed binary integer programming problem, which is difficult to solve. We provide a relaxed-rounding solution to the model. Numerical results illustrate that the proposed algorithm achieves superior performance in comparison to state-of-the-art methods in terms of system throughput and the rate gain for users.

A heterogeneous cellular network (HCN) is useful to increase the spectral and energy efficiency of wireless networks and to reduce the traffic load from the macro cell.The performance of the secondary user equipment (SUE) is affected by interference from the eNodeB (eNB) in a macro cell.To decrease the interference between the macro cell and the small cell, allocating resources properly is essential to an HCN.This study considers the scenario of a software-defined heterogeneous cellular network and performs the resource allocation process.First, we show the system model of HCN and formulate the optimization problem.The optimization problem is a complex process including power and frequency resource allocation, which imposes an extremely high complexity to the HCN.Therefore, a hierarchical resource allocation scheme is proposed, which including subchannel selection and a particle swarm optimization (PSO)-based power allocation algorithm.Simulation results show that the proposed hierarchical scheme is effective in improving the system capacity and energy efficiency.